1. Field of Invention
The invention relates to an apparatus for setting the throttle position in the air feed region of an internal combustion engine as a function of a desired torque, a device having at least two settings which can be switched over as a function of parameters and influence the degree of fill.
2. Description of Related Art
A known design of such a device is a so-called switchable suction pipe which has, for example, two feed channels of different length to the individual cylinders of the internal combustion engine in each case. The shorter feed channel is active in the higher speed range, and the longer one is active in the lower speed range, the switchover being performed by actuating a suction pipe flap. The feed channels of different length effect an improved degree of fill efficiency in the corresponding speed ranges, on the basis of resonance effects.
Since the switchover between the shorter and the longer feed channels would lead to a jump in torque, solutions have already been proposed to prevent this. One proposal is based on the principle of a suction pipe model, with the aid of which the change in degree of fill is simulated by a physical model. A disadvantage of this is the high computational outlay required therefor, and the fact that pressure pulsations, which participate largely in the change in degree of fill, cannot also be included. A further proposal is based on pilot control by means of a singular offset which is determined from a characteristic diagram dependent on the accelerator pedal/speed. One disadvantage of this proposal is the sudden change in the throttle angle, which scarcely deals with the real suction pipe dynamics. Jolting oscillations of the vehicle can occur as a consequence, and the failure to take account of the respectively most current accelerator pedal value and/or of the environmental influences (pressure, temperature) during the changeover operation can likewise lead to undesired fluctuations in degree of fill.
It is therefore the object of the present invention to create an apparatus of the generic type mentioned at beginning which achieves a comfortable switchover without jolting, self-acceleration of the vehicle and the like in conjunction with a low additional outlay on processor power and development costs.
The advantages of the apparatus according to the invention, reside, in particular, in the fact that it largely eliminates torque fluctuations in the case of switching operations of devices which influence degree of fill, the suction pipe flaps in switchable suction pipes, or also other actuators which influence degree of fill for the purpose of cylinder shut-down, valve switching or the like. Jolting of the vehicle which impairs comfort, or even self-acceleration during switchover operation can be effectively prevented. This is achieved by an extremely simple and cost-effective solution which necessitates only relatively low outlay on processor power. In this case, the vehicle always remains dynamically controllable, that is to say the torque desired by the driver or other electronic devices is continually taken into account. A further advantage consists in that there is no departure from an operating point optimised for efficiency, for example a lambda value of 1 and an optimum ignition angle are retained. This is achieved, in particular, also by virtue of the fact that weighted interpolation is carried out between the two characteristic diagrams during the switchover operation for a temporally limited period.
Advantageous developments and improvements of the apparatus specified in claim 1 are possible by means of the measures set forth in the subclaims.
The apparatus according to the invention can be applied in a particularly advantageous way in the case of a switchable suction pipe with a suction pipe flap which is switched over as a function of engine speed.
For the purpose of preferably linear conversion from one prescribed value into the other, in particular during a fixed prescribable period, in an advantageous design of the circuit a subtraction stage is constructed for forming the difference of the prescribed values and a multiplier stage is constructed for multiplying the difference value by a ramp function, the ramp function running in each case between the values 0 and 1, and an adder stage being designed for adding the output value of the multiplier stage to one of the prescribed values.
In order to prevent frequent switching to and fro in the speed transition range, the switchover operations between the positions are preferably affected by hysteresis.